Method and apparatus for video coding

ABSTRACT

According to an aspect of the disclosure, a method of video decoding is performed in a video decoder. In the method, coded information of a current block is received from a coded video bitstream. The coded information includes prediction information of the current block. A determination is made whether the current block is predicted using a neighboring reconstructed sample from a non-zero reference line based on the coded information. A primary transform type is determined based on the determination that the current block is predicted using the neighboring reconstructed sample from the non-zero reference line. A primary transform is performed for a transform block that is partitioned from the current block in accordance with the determined primary transform type.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of priority to U.S.Provisional Application No. 62/851,504, “TRANSFORM SCHEME FOR NON-ZEROREFERENCE LINES” filed on May 22, 2019, which is incorporated byreference be rein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided be rein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has specific bitraterequirements. For example, 11080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth and/or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless compression and lossy compression, as well as a combinationthereof can be employed. Lossless compression refers to techniques wherean exact copy of the original signal can be reconstructed from thecompressed original signal. When using lossy compression, thereconstructed signal may not be identical to the original signal, butthe distortion between original and reconstructed signals is smallenough to make the reconstructed signal useful for the intendedapplication. In the case of video, lossy compression is widely employed.The amount of distortion tolerated depends on the application; forexample, users of certain consumer streaming applications may toleratehigher distortion than users of television distribution applications.The compression ratio achievable can reflect that: higherallowable/tolerable distortion can yield higher compression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques are behenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is using reference data only from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submodel/parameter combination can have animpact in the coding efficiency gain through intra prediction, and socan the entropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 2 shows a schematic (201) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes receiving circuitry and processing circuitry.

According to an aspect of the disclosure, a method of video decoding isperformed in a video decoder. In the method, coded information of acurrent block is received from a coded video bitstream. The codedinformation includes prediction information of the current block. Adetermination is made whether the current block is predicted using aneighboring reconstructed sample from a non-zero reference line based onthe coded information. A primary transform type is determined based onthe determination that the current block is predicted using theneighboring reconstructed sample from the non-zero reference line. Aprimary transform is performed for a transform block that is partitionedfrom the current block in accordance with the determined primarytransform type.

In some embodiments, the current block can be predicted using theneighboring reconstructed sample from the non-zero reference line, andthe primary transform type can be a DCT-2 mode or a skip mode.

In some embodiments, the prediction information can include primarytransform type information. The primary transform type can be determinedbased on the primary transform type information. The primary transformtype can be determined to be the skip mode, responsive to the primarytransform type information indicating a first value, and the primarytransform type can be determined to be the DCT-2 mode, responsive to theprimary transform type information indicating a second value.

In some embodiments, a context model can be determined from a set ofcontext models based on the coded information, where the codedinformation indicates a reference line that includes the neighboringreconstructed sample. Primary transform type information can be decodedbased on the determined context model, where the primary transform typeinformation indicates whether the primary transform type is the skipmode or the DCT-2 mode.

In some embodiments, the current block can be predicted using theneighboring reconstructed sample from the non-zero reference line. Theprimary transform type further can include a horizontal transform typeand a vertical transform type. The horizontal transform type can be aDCT-2 mode or a DST-7 mode, and the vertical transform type can be theDCT-2 mode or the DST-7 mode.

In some embodiments, the horizontal transform type and/or the verticaltransform type can be dependent on a width or a height of the currentblock.

In some embodiments, the current block can be predicted using theneighboring reconstructed sample from the non-zero reference line. Thenon-zero reference line can be a reference line 1 or a reference line 3.The primary transform type can be a DST-7 mode, responsive to thenon-zero reference line being the reference line 1. The primarytransform type can be a DCT-2 mode, responsive to the non-zero referenceline being the reference line 3.

In some embodiments, secondary transform information can be received.The secondary transform information indicates whether a secondarytransformation is performed on the transform block. The secondarytransformation can be performed on the transform block, responsive to(i) the secondary transform information indicating that the secondarytransformation is performed on the transform block, and (ii) the currentblock being predicted using a neighboring reconstructed sample from azero reference line (or a reference line zero).

In some embodiments, a context model can be determined from a set ofcontext models based on the coded information, where the codedinformation indicates a reference line that includes the neighboringreconstructed sample. Secondary transform information can be decodedbased on the determined context model, where the secondary transforminformation indicates whether a secondary transformation is performed onthe transform block. The secondary transformation can be performed onthe transform block responsive to the secondary transform informationindicating the secondary transformation is performed on the transformblock.

In some embodiments, secondary transform information can be received,where the secondary transform information indicates whether a secondarytransformation is performed on the transform block. The secondarytransformation can be performed on the transform block, responsive to(i) the secondary transform information indicating that the secondarytransformation is performed on the transform block, and (ii) the currentblock being predicted using the neighboring reconstructed sample fromthe non-zero reference line, and (iii) a width and/or a height of thecurrent block is equal to or larger than a threshold.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 2 is an illustration of exemplary intra prediction directions.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 7 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 8 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 9 shows 35 intra prediction modes in accordance with an embodiment.

FIG. 10 shows 95 intra prediction modes in accordance with anembodiment.

FIG. 11 shows reference lines adjacent to a coding block unit inaccordance with an embodiment.

FIG. 12 shows a first exemplary division of blocks.

FIG. 13 shows a second exemplary division of blocks.

FIG. 14 shows an exemplary reduced secondary transform (RST).

FIG. 15A shows a forward reduced transform.

FIG. 15B shows an inverse reduced transform.

FIG. 16A shows a first exemplary embodiment of RST.

FIG. 16B shows a second exemplary embodiment of RST.

FIG. 17 shows a flow chart outlining a process example according to someembodiments of the disclosure.

FIG. 18 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the FIG. 3 example, the first pair of terminal devices (310) and(320) performs unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (330) and (340)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (330) and (340) via the network (350). Eachterminal device of the terminal devices (330) and (340) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (330) and (340), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 3 example, the terminal devices (310), (320), (330) and(340) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained be rein below.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403 ) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or encoded video bitstream (404)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anembodiment of the present disclosure. The video decoder (510) can beincluded in an electronic device (530). The electronic device (530) caninclude a receiver (531) (e.g., receiving circuitry). The video decoder(510) can be used in the place of the video decoder (410) in the FIG. 4example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (501), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (531) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (531) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (515) may be coupled inbetween the receiver (531) and an entropy decoder/parser (520) (“parser(520)” henceforth). In certain applications, the buffer memory (515) ispart of the video decoder (510). In others, it can be outside of thevideo decoder (510) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (510), forexample to combat network jitter, and in addition another buffer memory(515) inside the video decoder (510), for example to handle playouttiming. When the receiver (531) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (515) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the butler memory (515) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as was shown in FIG. 5. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (520). The flow of such subgroup control information between theparser (520) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (558). The currentpicture buffer (558) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(555), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (552) has generated to the outputsample information as provided by the scaler/inverse transform unit(551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, furexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anembodiment of the present disclosure. The video encoder (603) isincluded in an electronic device (620). The electronic device (620)includes a transmitter (640) (e.g., transmitting circuitry). The videoencoder (603) can be used in the place of the video encoder (403) in theFIG. 4 example.

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCh4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (650). In some embodiments, the controller(650) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (650) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (650) can be configured to have other suitablefunctions that pertain to the video encoder (603) optimized for acertain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (634). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (634) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5. Brieflyreferring also to FIG. 5, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously coded picture fromthe video sequence that were designated as “reference pictures.” In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art s aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one lama CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherembodiment of the disclosure. The video encoder (703) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (703) is used in theplace of the video encoder (403) in the FIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orhi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes the interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721), andan entropy encoder (725) coupled together as shown in FIG. 7.

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (722) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intramode, the general controller (721) controls the switch (726) to selectthe intra mode result for use by the residue calculator (723), andcontrols the entropy encoder (725) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(721) controls the switch (726) to select the inter prediction resultfor use by the residue calculator (723), and controls the entropyencoder (725) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (703) also includes a residuedecoder (728). The residue decoder (728) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (722) and theinter encoder (730). For example, the inter encoder (730) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (722) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (725) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 8 shows a diagram of a video decoder (810) according to anotherembodiment of the disclosure. The video decoder (810) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (810) is used in the place of the videodecoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8.

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (872) or the inter decoder (880), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or hi-predicted mode, the inter prediction information is providedto the inter decoder (880); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (872). The residual information can be subject to inversequantization and is provided to the residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extras de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (873) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (871) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (873) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603),and (703), and the video decoders (410), (510), and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

The present disclosure is directed to a set of advanced video codingtechnologies, including a transform scheme for non-zero reference lines.

A total of 35 intra prediction modes is illustrated in FIG. 9, forexample as used in HEVC. Among the 35 intra prediction modes, mode 10 isa horizontal mode and mode 26 is a vertical mode. Modes 2, 18, and 34are diagonal modes. The 35 intra prediction modes can be signalled bythree most probable modes (MPMs) and 32 remaining modes.

A total of 95 intra prediction modes is illustrated in FIG. 10, forexample as used in VVC. Mode 18 is a horizontal mode and mode 50 is avertical mode. Modes 2, 34, and 66 are diagonal modes. Modes −1 to −14and modes 67 to 80 can be referred to as Wide-Angle intra Prediction(WAIP) modes.

In multi-line intra prediction, additional reference lines can be usedfor intra prediction. An encoder can determine and signal whichreference line is used to generate the intra predictor. In one example,reference lines 0, 1, and 3 can be used, and reference line 2 can beexcluded. The reference line index can be signaled before intraprediction modes, and only the most probable modes can be allowed incase a nonzero reference line index is signaled. In FIG. 11, an exampleof 4 reference lines (e.g., reference lines 0-3) is depicted, where eachof the four reference lines is composed of six segments, i.e., SegmentsA to F, together with the top-left reference sample. In addition, theSegments A and F can be padded with the closest samples from theSegments B and E, respectively.

An Intra Sub-Partitions (ISP) coding mode divides lama intra-predictedblocks vertically or horizontally into 2 or 4 sub-partitions dependingon the block size dimensions, as shown in Table 1 for example. FIGS. 12and 13 show two exemplary possibilities. FIG. 12 illustrates anexemplary division that can be applied to 4×8 and 8×4 blocks. FIG. 13illustrates an exemplary division that can be applied to all blocksexcept 4×8, 8×4, and 4×4 blocks. It should be noted that allsub-partitions fulfill the condition of having at least 16 samples as anexample.

TABLE 1 Number of sub-partitions depending on the block size Block SizeNumber of Sub-Partitions 4 × 4 Not divided 4 × 8 and 8 × 4 2 All othercases 4

For each sub-partition, a residual signal can be generated by entropydecoding coefficients sent by the encoder. The coefficients are inversequantized and inverse transformed. A sub-partition can be subsequentlyintra predicted to generate a prediction signal and correspondingreconstructed samples of the sub-partition can be obtained by adding theresidual signal to the prediction signal. Therefore, the reconstructedvalues of each of the sub-partitions can be available to generate theprediction of a next sub-partition. This process mentioned above can berepeated for the other sub-partitions. In addition, all sub-partitionscan share a same intra mode.

Based on the intra mode and the split utilized, two different classes ofprocessing orders can be used, which can be referred to as a normalprocessing order and a reversed processing order. In the normalprocessing order, a first sub-partition to be processed is the onecontaining the top-left sample of the CU and then the normal processingorder continues downwards (e.g., for a horizontal split) or rightwards(e.g., for a vertical split). As a result, reference samples used togenerate the sub-partition prediction signals can only be located at theleft and above sides of the reference lines. On the other hand, thereverse processing order can either start with a sub-partitioncontaining the bottom-left sample of the CU and continues upwards orstart with a sub-partition containing the top-right sample of the CU andcontinues leftwards.

The ISP algorithm is only tested with intra modes that are part of theMPM list in some embodiments. For this reason, if a block uses ISP, theMPM flag can be inferred to be one. In addition, if ISP is used for acertain block, the MPM list can be modified to exclude the DC mode, andto prioritize horizontal intra modes for the ISP horizontal split andvertical infra modes for the vertical split.

Besides 4-point, 8-point, 16-point and 32-point DCT-2 transforms whichare applied in HEVC, additional 2-point and 64-point DCT-2 can also beincluded, in VVC for example. All the primary transform matrices in VVCcan be used with 8-bit representation. Adaptive Multiple Transforms(AMT) can be applied to the CUs with both a width and a height smallerthan or equal to 32, and whether AMT applies or not to the CUs can becontrolled by a flag called mts_flag. For example, when the mts_flag isequal to 0, only DCT-2 is applied for coding the residue. When themts_flag is equal to 1, an index mts idx can further be signalled using2 bins to identify the horizontal and vertical transform to be usedaccording to Table 2, where value 1 means using DST-7 and value 2 meansusing DCT-8 for example.

When both the height and width of the coding block is smaller than orequal to 64, the transform size can always the same as the coding blocksize, such as in VVC. When either the height or width of the codingblock is larger than 64, during the operation of the transform or intraprediction, the coding block can further be split into multiplesub-blocks, where the width and the height of each sub-block is smallerthan or equal to 64, and one transform is performed on each sub-block.

In JVET-M0464, a modified syntax design for transform skip and MTS hasbeen proposed and adopted into VVC Draft 3. The following Table 2illustrates the modified syntax of the proposed joint syntax elementtu_mts_jdx compared to VVC Draft 3.

TABLE 2 a modified syntax including a joint syntax element tu_mts_idxVVC Draft 3 Proposed method in JVET-M0464 transform_unit( )transform_unit( )  tu_cbf_luma  tu_cbf_luma ...  if( ... tu_cbf_luma && if( ... tu_cbf_luma &&   ( tbWidth <= 32 ) &&   ( tbWidth <= 32 ) &&  ( tbHeight <= 32 ) ... )   ( tbHeight <= 32 ) ... )   tu_mts_flag  tu_mts_idx residual_coding( cIdx )  if( ( cIdx ! = 0 | | !tu_mts_flag) &&   ( log2TbWidth <= 2 ) &&   ( log2TbHeight <= 2 ) )  transform_skip_flag[ cIdx ]  ... /* coefficient parsing */ ...  if(tu_mts_flag && cIdx = = 0 )   mts_idx

In Table 2, mts_idx[x0][y0] specifies which transform kernels areapplied to the luma residual samples along the horizontal and verticaldirection of the current transform block. The array indices x0, y0specify the location (x0, y0) of the top-left luma sample of theconsidered transform block relative to the top-left luma sample of thepicture.

In addition, transform_skip_flag[x0][y0][cIdx] specifies whether atransform is applied to the associated transform block or not. The arrayindices x0, y0 specify the location (x0, y0) of the top-left luma sampleof the considered transform block relative to the top-left luma sampleof the picture. The array index cIdx specifies an indicator for thecolor component. The array index cIdx can be equal to 0 for luma, equalto 1 for Cb and equal to 2 for Cr, transform_skip_flag[x0][y0][cIdx]equal to 1 specifies that no transform is applied to the currenttransform block transform_skip_flag[x0][y0][cIdx] equal to 0 specifiesthat the decision whether transform is applied to the current transformblock or not depends on other syntax elements. Whentransform_skip_flag[x0][y0][cIdx] j is not present, thetransform_skip_flag[x0][y0][cIdx] is inferred to be equal to 0.

Instead of parsing the MTS flag first, then parsing the TS flag, andfollowed by fixed length coding with 2 bins for the MTS index, the newjoint syntax element_tu_mts_idx uses truncated unary binarization. Thefirst bin indicates TS (or transform skip), the second bin indicates MTSand all following bins indicate the MTS index. Examples of the semanticsand binarization is shown in Table 3.

TABLE 3 tu_mts_idx using truncated unary binarization transform typebinarization MTS & TS MTS TS tu_mts_idx horizontal vertical enabledenabled enabled 0 SKIP SKIP 0 — 0 1 DCT-2 DCT-2 10 0 1 2 DST-7 DST-7 11010 — 3 DCT-8 DST-7 1110 110 — 4 DST-7 DCT-8 11110 1110 — 5 DCT-8 DCT-811111 1111 —

When the number of context models is not changed, the assignment of thecontext index increment ctxInc to each bin of to mts idx can be shown inTable 4. As shown in Table 4, the ctxInc can have values that include0-9, and na, which correspond to values of binIdx (e.g., 0, 1, 2, 3, 4,>=5).

TABLE 4 an assignment of the context index increment ctxInc to each binof tu_mts_idx binIdx Syntax element 0 1 2 3 4 >=5 tu_mts_idx 0 1 . . . 67 8 9 na (MTS & TS) (1 + cqtDepth) tu_mts_idx 1 . . . 6 7 8 9 na na(MTS) (1 + cqtDepth) tu_mts_idx 0 na na na na na (TS)

A mode-dependent non-separable secondary transform (NSST) can be appliedbetween the forward core transform and quantization (e.g., at theencoder) and between the de-quantization and inverse core transform(e.g., at the decoder). To reduce complexity, NSST is only applied tothe low frequency coefficients after the primary transform for example.If both a width (W) and a height (H) of a transform coefficient blockare larger than or equal to 8, then 8×8 non-separable secondarytransform can be applied to the top-left 8×8 region of the transformcoefficients block. Otherwise, if either a W or a H of a transformcoefficient block is equal to 4, a 4×4 non-separable secondary transformcan be applied and the 4×4 non-separable transform is performed on thetop-left min(8,W)×min(8,H) region of the transform coefficient block.The above transform selection rule can be applied for both luma andchroma components.

Matrix multiplication implementation of a non-separable transform can bedescribed as follows using a 4×4 input block X as an example. To applythe non-separable transform, the 4×4 input block X

$\begin{matrix}{X = \begin{bmatrix}X_{00} & X_{01} & X_{02} & X_{03} \\X_{10} & X_{11} & X_{12} & X_{13} \\X_{20} & X_{21} & X_{22} & X_{23} \\X_{30} & X_{31} & X_{32} & X_{33}\end{bmatrix}} & \left( {{Eq}.\mspace{11mu} 1} \right)\end{matrix}$

-   is represented as a vector {right arrow over (X)}:-   {right arrow over (X)}=[X₀₀ X₀₁ X₀₂ X₀₃ X₁₀ X₁₁ X₁₂ X₁₃ X₂₀ X₂₁ X₂₂    X₂₃ X₃₀ X₃₁ X₃₂ X₃₃]^(T)

The non-separable transform is calculated as {right arrow over(F)}=T·{right arrow over (X)}, where {right arrow over (F)} indicatesthe transform coefficient vector, and T is a 16×16 transform matrix. The16×1 coefficient vector {right arrow over (F)} is subsequentlyre-organized as a 4×4 block using the scanning order for that block(e.g., horizontal, vertical, or diagonal). The coefficients with asmaller index can be placed with the smaller scanning index in the 4×4coefficient block. A Hypercube-Givens Transform (HyGT) with a butterflyimplementation can be used instead of matrix multiplication to reducethe complexity of non-separable transform, for example in JEM.

In one embodiment, 35×3 non-separable secondary transforms can beutilized in a design of NSST for both 4×4 and 8×8 block sizes, where 35is the number of transform sets specified by the intra prediction mode,denoted as set, and 3 is the number of NSST candidates for each intraprediction mode. The mapping from the intra prediction mode to thetransform set can be defined in Table 5. The transform set applied toluma/chroma transform coefficients is specified by the correspondingluma/chroma intra prediction modes, according to Table 5 for example.For intra prediction modes larger than 34 (e.g., diagonal predictiondirection), the transform coefficient block can be transposed beforeand/or after the secondary transform at the encoder and/or decoder.

For each transform set, the selected non-separable secondary transformcandidate can further be specified by the explicitly signalled CU-levelNSST index. The index is signalled in a bitstream once per intra CUafter transform coefficients and truncated unary binarization is used.The truncated value is 2 in case of planar or DC mode, and 3 for angularintra prediction mode. The CU-level NSST index is signalled only whenmore than one non-zero coefficient is positioned in a CU. The defaultvalue of the CU-level NSST index is zero when the CU-level NSST index isnot signalled. A zero value of the CU-level NSST index indicatessecondary transform is not applied to the current CU, and other values(e.g., values 1-3) can indicate which secondary transform from the setshould be applied.

In some embodiments, NSST may not be applied for a block coded withtransform skip mode. When the NSST index is signalled for a CU and notequal to zero, NSST is not used for a block of a component that is codedwith transform skip mode in the CU. When a CU with blocks of allcomponents are coded in transform skip mode or the number of non-zerocoefficients of non-transform-skip mode CBs is less than 2, the NSSTindex is not signalled for the CU.

Reduced Size Transform (RST) is a variant of NSST using a transformzero-out scheme, which is also named as Low Frequency Non SeparableTransform (LFNST), has been proposed in JVET-N0193. The RST checkswhether the intra prediction mode is Planar or DC for entropy coding thetransform index of NSST.

In JVET-N0193, for example, four transform sets are applied, and eachtransform set includes three RST transform cores, which can be eithersize 16×48 (e.g., applied for a transform coefficient block with aheight and a width both being greater than or equal to 8) or 16×16(e.g., applied for a transform coefficient block with either the heightor the width being equal to 4). For rotational convenience, the 16×64(or 16×48) transform is denoted as RST8×8 and the 16×16 transform isdenoted as RST4×4. FIG. 14 shows an exemplary RST8×8 that has a RSTusing a 16×64 secondary transform core.

For the computation of RST, the main idea of a Reduced Transform (RT) isto map an N dimensional vector to an R dimensional vector in a differentspace, where R/N (R<N) is the reduction factor. The RT matrix is an R×Nmatrix as follows:

$\begin{matrix}{T_{RxN} = \begin{bmatrix}t_{11} & t_{12} & t_{13} & \ldots & t_{1N} \\t_{21} & t_{22} & t_{23} & \ldots & t_{2N} \\\vdots & \vdots & \vdots & \ddots & \vdots \\t_{R\; 1} & t_{R\; 2} & t_{R\; 3} & \ldots & t_{RN}\end{bmatrix}} & \left( {{Eq}.\mspace{11mu} 2} \right)\end{matrix}$

where the R rows of the transform are R bases of the N dimensionalspace. The inverse transform matrix for RT is the transpose of itsforward transform. The forward and inverse RT can be depicted in FIGS.15A and 15B. FIG. 15A is a schematic view of a forward reduced transformand FIG. 15B is a schematic view of a reduced inverse transform.

The RST8×8 with a reduction factor of 4 (¼ size) can be applied. Hence,instead of 64×64, which is a conventional 8×8 non-separable transformmatrix size, a 16×64 direct matrix can be used. In other words, the64×16 inverse RST matrix can be used at the decoder side to generatecore (primary) transform coefficients in 8×8 top-left regions. Theforward RST8×8 uses 16×64 (or 8×64 for 8×8 block) matrices so that theforward RST8×8 produces non-zero coefficients only in the top-left 4×4region within the given 8×8 region. In other words, if RST is appliedthen the 8×8 region except its top-left 4×4 region can have only zerocoefficients. For RST4×4, 16×16 (or 8×16 for 4×4 block) direct matrixmultiplication can be applied.

In addition, for RST8×8, to further reduce the transform matrix size,instead of using the whole top-left 8×8 coefficients as inputs forcalculating the secondary transform, the top-left three 4×4 coefficientscan be used as the inputs for calculating the secondary transform. FIGS.16A-16B show different alternatives of RST8×8. FIG. 16A shows an exampleof 16×64 transform matrices and the whole top-left 8×8 coefficients areapplied as inputs for calculating the secondary transform. FIG. 16Bshows an example of 16×48 transform matrices and the top-left three 4×4coefficients are used as the inputs for calculating the secondarytransform.

An inverse RST can be conditionally applied when the following twoconditions are satisfied: (a) block size is greater than or equal to agiven threshold (width>=4 && height>=4); and (b) transform skip modeflag is equal to zero.

If both a width (W) and a height (H) of a transform coefficient blockare greater than 4, then the RST8×8 can be applied to the top-left 8×8region of the transform coefficient block. Otherwise, the RST4×4 can beapplied on the top-left min(8, W)×min(8, H) region of the transformcoefficient block.

In an embodiment, if a RST index is equal to 0, RST is not applied.Otherwise, RST is applied, and a corresponding kernel (or transform set)is chosen in accordance with the RST index. Furthermore, RST can beapplied for an intra CU in both intra and inter slices, and for bothLuma and Chroma. If a dual tree is enabled, RST indices for Luma andChroma can be signaled separately. For inter slice (the dual tree isdisabled), a single RST index can be signaled and used for both Luma andChroma. When ISP mode is selected, RST is disabled and RST index is notsignaled.

For the derivation of an RST transform set, an RST matrix can be chosenfrom four transform sets, and each of the four transform sets caninclude (or consist of) two transforms. Which transform set is appliedcan be determined from an intra prediction mode as follows: (a) If oneof three Cross-component Linear Model (CCLM) modes is indicated,transform set 0 is selected; (b) Otherwise, transform set selection isperformed according to Table 5.

TABLE 5 The transform set selection table Tr. set IntraPredMode indexIntraPredMode < 0 1 0 <= IntraPredMode <= 1 0 2 <= IntraPredMode <= 12 113 <= IntraPredMode <= 23 2 24 <= IntraPredMode <= 44 3 45 <=IntraPredMode <= 55 2 56 <= IntraPredMode 1

As shown in Table 5, an index IntraPredMode can have a range of [−14,83], which is a transformed mode index used for wide angle intraprediction. An index Tr. set index can have a group of values thatcorrespond to the range of the index IntraPredMode.

Currently in VTM5.0, a same transform scheme is applied whether or not acurrent block is predicted by using neighboring reconstructed samplesfrom a zero-reference line or non-zero reference lines. However, aresidual energy distribution is different for these two cases.Therefore, it may be not desirable to use the same transform scheme forboth two cases.

In the disclosure, the term block may be interpreted as a predictionblock, a coding block, or a coding unit (CU). The line index of thenearest reference line is 0 (zero reference line or adjacent referenceline), and other lines are called non-zero reference lines (ornon-adjacent reference lines).

In the disclosure, different transform schemes can be applied on acurrent block when the current block is predicted using one or moreneighboring reconstructed samples from zero-reference line and non-zeroreference lines.

In some embodiments, Multiple Transform Selection (MTS) (or DST-7 and/orDCT-8) is disabled for the current block when the current block ispredicted using neighboring samples (or neighboring reconstructedsamples) from non-zero reference lines. In some embodiments, thenon-zero reference lines can include a reference line 1 and referenceline 3. In some embodiments, the current block can be predicted usingone or more neighboring samples from the reference line 1. In someembodiments the current block can be predicted using one or moreneighboring samples from the reference line 3. In some embodiments, thecurrent block can be predicted using neighboring samples from thereference line 1 and the reference line 3. In an embodiment, whentransform skip mode is allowed, tu_mts_idx can be 0 or 1 for non-zeroreference lines, and one bin can be signaled to indicate whether atransform skip (TS) mode is used or not. Table 6 illustrates exemplaryvalues of the tu_mts_idx and corresponding transform modes.

TABLE 6 The values of the tu_mts_idx and corresponding transform modestransform type binarization tu_mts_idx horizontal vertical TS enabled TSdisabled 0 SKIP SKIP 0 — 1 DCT-2 DCT-2 1 0

As shown in Table 6, when tu_mts_idx is equal to 0, the transform skipmode can be applied for both a horizontal transform and a verticaltransform of transform blocks partitioned form the current block. Whentu_mts_idx is equal to 1, a predetermined transform mode (e.g., DCT-2transform mode (also referred to as DCT-2)) can be applied for both thehorizontal transform and the vertical transform of the transform blocks.Still referring to Table 6, binarization values can be used to indicatewhether the TS mode is enabled. For example, binarization 0 indicatesthat the TS mode is enabled in response to the tu_mts_idx being 0.

In an embodiment, a context used for entropy coding tu_mts_idx candepend on a reference line index. At the decoder side, the decoder candetermine a context model from a set of context models according to areference line associated with the reference line index, and thereference line includes at least one neighboring reconstructed sample ofthe current block. A value (e.g., 0 or 1) of the tu_mts_idx can bedecoded, and a primary transform type (e.g., the transform skip mode orthe DCT-2 transform mode) can be determined according to the value ofthe tu_mts_idx.

In an embodiment, when the transform skip mode is disabled, only apredetermined transform mode (e.g., the DCT-2 transform mode) can beapplied (i.e., tu_mts_idx can only be 1) for non-zero reference lines.

In an embodiment, both the horizontal and/or vertical transform type canbe set to DST-7 when the current block is predicted by the neighboringreconstructed samples from non-zero reference lines.

In an embodiment, the horizontal and/or vertical transform type can onlybe a predetermined transform mode (e.g., DCT-2 or DST-7) when thecurrent block is predicted by the neighboring reconstructed samples fromnon-zero reference lines.

In an embodiment, the horizontal and/or vertical transform type isdependent on a width or a height of the current block when the currentblock is predicted by the neighboring reconstructed samples fromnon-zero reference lines. In an example, when the width (or the height)of the current block is equal to or larger than 4 pixels and equal to orless than 16 pixels, the horizontal (or vertical) transform type is setto a first transform mode (e.g., DST-7). Otherwise, the horizontal (orvertical) transform type is set to a second transform mode (e.g.,DCT-2).

In an embodiment, different transform modes can be used for differentnon-zero reference lines. For example, a first transform mode (e.g.DST-7) can be only used for the reference line I, and a second transformmode (e.g., DCT-2) can be only used for the reference line 3.

In some embodiments, TS (or transform skip) can be disabled for thecurrent block when the current block is predicted using the neighboringsamples from non-zero reference lines. In an example, only apredetermined transform mode (e.g., DCT-2) is applied when the currentblock is predicted using the neighboring samples from non-zero referencelines and the transform type (e.g., tu_mts_idx) is not signaled.

In some embodiments, LFNST can be disabled for the current block whenthe current block is predicted using the neighboring samples fromnon-zero reference lines. A context used for entropy coding a LFNSTindex can depend on a reference line index, where the LFNST indexindicates whether the LFNST is performed on the transform blockspartitioned form the current block.

In some embodiments, if the current block is predicted using theneighboring reconstructed samples from non-zero reference lines, LFNSTcan be only applied when the width and/or the height of the currentblock satisfies a certain condition. For example, if the current blockis predicted using the neighboring reconstructed samples from non-zeroreference lines, LFNST is only applied when the width and/or the heightof the current block is equal to or larger than a threshold value. Thethreshold value can be a positive integer, such as 8 pixels or 16pixels.

FIG. 17 shows a flow chart outlining a process (1700) according to anembodiment of the disclosure. The process (1700) can be used in thereconstruction of a block, so to generate a prediction block for theblock under reconstruction. In various embodiments, the process (1700)are executed by processing circuitry, such as the processing circuitryin the terminal devices (310), (320), (330) and (340), the processingcircuitry that performs functions of the video encoder (403), theprocessing circuitry that performs functions of the video decoder (410),the processing circuitry that performs functions of the video decoder(510), the processing circuitry that performs functions of the videoencoder (603), and the like. In some embodiments, the process (1700) isimplemented in software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (1700). The process starts at (S1701) and proceeds to(S1710).

As show in FIG. 17, the process 1700 can start with (S1710), where codedinformation of a current block can be received from a coded videobitstream. The coded information includes prediction information of thecurrent block.

At (S1720), a determination is made as to whether the current block ispredicted using a neighboring reconstructed sample from a non-zeroreference line based on the coded information. The non-zero referenceline can be a reference line I or a reference line 3, for example.

At (S1730), a primary transform type can be determined based on thedetermination that the current block is predicted using the neighboringreconstructed sample from the non-zero reference line. The neighboringreconstructed sample can be one of a plurality of neighboringreconstructed samples used to predict the current block. Further, theplurality of neighboring reconstructed samples can be included in thesame non-zero reference line or one or more different reference lines.In some embodiments, the primary transform type can be a DCT-2 mode or askip mode. In some embodiments, the prediction information can includeprimary transform type information (e.g., tu_mts_idx). The primarytransform type can be determined based on the primary transform typeinformation. The primary transform type can be determined to be the skipmode, responsive to the primary transform type information indicating afirst value, and the primary transform type can be determined to be theDCT-2 mode, responsive to the primary transform type informationindicating a second value. In some embodiments, a context model can bedetermined from a set of context models based on the coded information,where the coded information indicates a reference line that includes theneighboring reconstructed sample. The primary transform type informationcan be decoded based on the determined context model, where the primarytransform type information indicates whether the primary transform typeis the skip mode or the DCT-2 mode.

At (S1740), a primary transform can be performed for a transform blockthat is partitioned from the current block in accordance with thedetermined primary transform type.

The embodiments described be rein can be used separately or combined inany order. Further, each of the embodiments, encoder, and decoder may beimplemented by processing circuitry (e.g., one or more processors or oneor more integrated circuits). In one example, the one or more processorsexecute a program that is stored in a non-transitory computer-readablemedium.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 18 shows a computersystem (1800) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 18 for computer system (1800) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1800).

Computer system (1800) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1801), mouse (1802), trackpad (1803), touchscreen (1810), data-glove (not shown), joystick (1805), microphone(1806), scanner (1807), camera (1808).

Computer system (1800) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1810), data-glove (not shown), or joystick (1805), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1809), be headphones(not depicted)), visual output devices (such as screens (1810) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1800) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1820) with CD/DVD or the like media (1821), thumb-drive (1822),removable hard drive or solid state drive (1823), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1800) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1849) (such as, for example USB ports of thecomputer system (1800)); others are commonly integrated into the core ofthe computer system (1800) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1800) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1840) of thecomputer system (1800).

The core (1840) can include one or more Central Processing Units (CPU)(1841), Graphics Processing Units (GPU) (1842), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1843), hardware accelerators for certain tasks (1844), and so forth.These devices, along with Read-only memory (ROM) (1845), Random-accessmemory (1846), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1847), may be connectedthrough a system bus (1848). In some computer systems, the system bus(1848) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1848),or through a peripheral bus (1849). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1841), GPUs (1842), FPGAs (1843), and accelerators (1844) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1845) or RAM (1846). Transitional data can be also be stored in RAM(1846), whereas permanent data can be stored for example, in theinternal mass storage (1847). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1841), GPU (1842), massstorage (1847), ROM (1845), RAM (1846), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1800), and specifically the core (1840) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1840) that are of non-transitorynature, such as core-internal mass storage (1847) or ROM (1845). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1840). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1840) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described be rein, including defining datastructures stored in RAM (1846) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1844)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described be rein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

-   Appendix A: Acronyms-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Di splay-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described be rein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of video decoding performed in a videodecoder, the method comprising: receiving coded information of a currentblock from a coded video bitstream, the coded information comprisingprediction information of the current block; determining whether thecurrent block is predicted using a neighboring reconstructed sample froma non-zero reference line based on the coded information; determining aprimary transform type based on the determination that the current blockis predicted using the neighboring reconstructed sample from thenon-zero reference line; and performing a primary transform for atransform block that is partitioned from the current block in accordancewith the determined primary transform type.
 2. The method of claim 1,wherein: the current block is predicted using the neighboringreconstructed sample from the non-zero reference line, and the primarytransform type is a DCT-2 mode or a skip mode.
 3. The method of claim 2,wherein the prediction information includes primary transform typeinformation, the determining the primary transform type includesdetermining the primary transform type based on the primary transformtype information, the primary transform type is determined to be theskip mode, responsive to the primary transform type informationindicating a first value, and the primary transform type is determinedto be the DCT-2 mode, responsive to the primary transform typeinformation indicating a second value.
 4. The method of claim 2, furthercomprising: determining a context model from a set of context modelsbased on the coded information, the coded information indicating areference line that includes the neighboring reconstructed sample; anddecoding primary transform type information based on the determinedcontext model, the primary transform type information indicating whetherthe primary transform type is the skip mode or the DCT-2 mode.
 5. Themethod of claim 1, wherein: the current block is predicted using theneighboring reconstructed sample from the non-zero reference line, andthe primary transform type further comprises a horizontal transform typeand a vertical transform type, the horizontal transform type being aDCT-2 mode or a DST-7 mode and the vertical transform type being theDCT-2 mode or the DST-7 mode.
 6. The method of claim 5, wherein thehorizontal transform type and/or the vertical transform type aredependent on a width or a height of the current block.
 7. The method ofclaim 1, wherein: the current block is predicted using the neighboringreconstructed sample from the non-zero reference line, the non-zeroreference line being a reference line 1 or a reference line 3, theprimary transform type is a DST-7 mode, responsive to the non-zeroreference line being the reference line 1, and the primary transformtype is a DCT-2 mode, responsive to the non-zero reference line beingthe reference line
 3. 8. The method of claim 1, further comprising:receiving secondary transform information that indicates whether asecondary transformation is performed on the transform block; andperforming the secondary transformation on the transform block,responsive to (i) the secondary transform information indicating thatthe secondary transformation is performed on the transform block, and(ii) the current block being predicted using a neighboring reconstructedsample from a zero reference line.
 9. The method of claim 1, furthercomprising: determining a context model from a set of context modelsbased on the coded information, the coded information indicating areference line that includes the neighboring reconstructed sample;decoding secondary transform information based on the determined contextmodel, the secondary transform information indicating whether asecondary transformation is performed on the transform block; andperforming the secondary transformation on the transform blockresponsive to the secondary transform information indicating thesecondary transformation is performed on the transform block.
 10. Themethod of claim 1, further comprising: receiving secondary transforminformation, the secondary transform information indicating whether asecondary transformation is performed on the transform block; andperforming the secondary transformation on the transform block,responsive to (i) the secondary transform information indicating thatthe secondary transformation is performed on the transform block, and(ii) the current block being predicted using the neighboringreconstructed sample from the non-zero reference line, and (iii) a widthand/or a height of the current block is equal to or larger than athreshold.
 11. An apparatus for video decoding, comprising: processingcircuitry configured to: receive coded information of a current blockfrom a coded video bitstream, the coded information comprisingprediction information of the current block; determine whether thecurrent block is predicted using a neighboring reconstructed sample froma non-zero reference line based on the coded information; determine aprimary transform type based on the determination that the current blockis predicted using neighboring reconstructed sample from the non-zeroreference line; and perform a primary transform for a transform blockthat is partitioned from the current block in accordance with thedetermined primary transform type.
 12. The apparatus of claim 11,wherein: the current block is predicted using the neighboringreconstructed sample from the non-zero reference line, and the primarytransform type is a DCT-2 mode or a skip mode.
 13. The apparatus ofclaim 12, wherein: the prediction information includes primary transformtype information, the primary transform type is determined based on theprimary transform type information, the primary transform type isdetermined to be the skip mode, responsive to the primary transform typeinformation indicating a first value, and the primary transform type isdetermined to be the DCT-2 mode, responsive to the primary transformtype information indicating a second value.
 14. The apparatus of claim12, wherein the processing circuitry is further configured to: determinea context model from a set of context models based on the codedinformation, the coded information indicating a reference line thatincludes the neighboring reconstructed sample; and decode primarytransform type information based on the determined context model, theprimary transform type information indicating whether the primarytransform type is the skip mode or the DCT-2 mode.
 15. The apparatus ofclaim 11, wherein: the current block is predicted using the neighboringreconstructed sample from the non-zero reference line, and the primarytransform type further comprises a horizontal transform type and avertical transform type, the horizontal transform type being a DCT-2mode or a DST-7 mode and the vertical transform type being the DCT-2mode or the DST-7 mode.
 16. The apparatus of claim 15, wherein thehorizontal transform type and/or the vertical transform type aredependent on a width or a height of the current block.
 17. The apparatusof claim 11, wherein: the current block is predicted using theneighboring reconstructed sample from the non-zero reference line, thenon-zero reference line being a reference line 1 or a reference line 3,the primary transform type is a DST-7 mode, responsive to the non-zeroreference line being the reference line 1, and the primary transformtype is a DCT-2 mode, responsive to the non-zero reference line beingthe reference line
 3. 18. The apparatus of claim 11, the processingcircuitry is further configured to: receive secondary transforminformation that indicates whether a secondary transformation isperformed on the transform block; and perform the secondarytransformation on the transform block, responsive to (i) the secondarytransform information indicating that the secondary transformation isperformed on the transform block, and (ii) the current block beingpredicted using a neighboring reconstructed sample from a zero referenceline.
 19. The apparatus of claim 11, wherein the processing circuitry isfurther configured to: determine a context model from a set of contextmodels based on the coded information, the coded information indicatinga reference line that includes the neighboring reconstructed sample;decode secondary transform information based on the determined contextmodel, the secondary transform information indicating whether asecondary transformation is performed on the transform block; andperform the secondary transformation on the transform block responsiveto the secondary transform information indicating the secondarytransformation is performed on the transform block.
 20. A non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform: receivingcoded information of a current block from a coded video bitstream, thecoded information comprising prediction information of the currentblock; determining whether the current block is predicted using aneighboring reconstructed sample from a non-zero reference line based onthe coded information; determining a primary transform type based on thedetermination that the current block is predicted using the neighboringreconstructed sample from the non-zero reference line; and performing aprimary transform for a transform block that is partitioned from thecurrent block in accordance with the determined primary transform type.